The sea urchin test system has been determined in our laboratory to be an extremely informative bioassay for pollutants, occurring as individual or as mixtures of xenobiotics. Harmful agents may be identified and characterized biologically to give an integrated set of data dealing with several key events, such as fertilization, mitotic activity, and embryogenesis. Therefore this bioassay may contribute to the assessment of the environmental impact of pollutants, by focusing on several important toxicological aspects.
This study was carried out on some inorganic pollutants [Cd(II), Cu(II), Zn(II), and Se(IV)] and their mixtures. Sublethal pH changes were taken into account as an additional stressor, capable of influencing the toxicities of tested agents. The experiments were performed on Paracentrotus lividus sperm and embryos, and on Echinus esculentus sperm. The results showed distinct patterns of embryotoxicity for the agents tested, which resulted in developmental defects as relatively high levels (>10−5 kmol/m3) for Cd(II) and Se(IV), whereas the embryotoxic effects of Cu(II) and Zn(II) were exerted at lower concentrations (5 × 10−7 kmol/m3) close to their natural seawater levels. Cytogenetic analysis of exposed embryos failed to reveal any morphological or quantitative changes in mitotic activity, at embryotoxic levels of all tested contaminants. The fertilization success of exposed sperm showed peculiar dose-response changes, as a result of the specific contaminant levels and of the simultaneous presence of other contaminants. Specifically, slight increases in Cd(II) or Cu(II) levels enhanced fertilization success, up to critical levels (10−7 to 10−6 kmol/m3); however, further increases in these metal ion concentrations led to a drop in fertilization success. The simultaneous presence of Zn(II) or Se(IV) dramatically changed the dose-response patterns, depending on the different mixtures and the test species.
The results may represent an example of the need to account for the simultaneous presence of several pollutants, whose combined impacts may be substantially different from those of the individual toxins. Moreover, the results attest to the high sensitivity of the sea urchin bioassay, which responds to very slight increases in microelements or contaminant levels above their natural concentrations.